Adjustment mechanism for charged particle beam apparatus

ABSTRACT

An adjustment mechanism for a charged particle beam apparatus which comprises a support surface disposed within the apparatus perpendicular to the beam axis, and a specimen holder disposed on the support surface and moveable transversely with respect to the beam axis. The holder includes apertures extending therethrough in a direction parallel to the beam axis which receive bearing means which engage the support surface. The bearing means have a dimension which is greater than that of the specimen holder in the direction of the beam axis and less than that of the apertures in the direction perpendicular to the beam axis. A coupling plate is disposed on the bearing means adjacent the specimen holder, and is coupled to adjusting means which is operable externally of the apparatus for adjusting the position of the plate, and thereby the position of the holder, with respect to the beam axis.

United States Patent von Ranch 1 Sept. 30, 1975 1 ADJUSTMENT MECHANISM FOR [73] Assignee: Siemens Aktiengesellschaft, Munich Germany 22 Filed: Feb. 20, 1974 [21] Appl.No.:443,946

[30] Foreign Application Priority Data Feb. 27 1973 Germany N 2310355 [52] US. Cl. 250/306; 250/440; 250/442 [51] Int. Cl. HOL] 37/20 [58] Field of Search 250/306, 3 l0, 3t l, 440, 250/441 442 [56] References Cited UNITED STATES PATENTS 3,426.193 2/l969 Guernet i. 250/442 3 628.()l3 l2/l97l Heide 250/442 Primary E.\'amim'rDavis Li Willis Attorney, Agent, or FirmKenyon & Kenyon Reilly Carr & Chapin [57] ABSTRACT An adjustment mechanism for a charged particle beam apparatus which comprises a support surface disposed within the apparatus perpendicular to the beam axis, and a specimen holder disposed on the support surface and moveablc transversely with respect to the beam axis The holder includes apertures extending therethrough in a direction parallel to the beam axis which receive bearing means which engage the support surface The bearing means have a dimension which is greater than that of the specimen holder in the direction of the beam axis and less than that of the apertures in the direction perpendicular to the beam axis. A coupling plate is disposed on the bearing means adjacent the specimen holder, and is coupled to adjusting means which is operable externally of the apparatus for adjusting the position of the plate. and thereby the position of the holder. with respect to the beam axis.

2 Claims, 2 Drawing Figures ADJUSTMENT MECHANISM FOR CHARGED PARTICLE BEAM APPARATUS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates generally to charged particle beam apparatus, such as electron microscopes, and in particular to an adjustment mechanism for positioning the specimen holder of such an apparatus with respect to the particle beam axis.

2. Description of the Prior Art Specimen holder adjustment devices for charged particle beam apparatus are generally known in the art. Such devices have the disadvantage that the image pro jected by the apparatus is frequently instable. In Volume 24 of Mikmskopie (I969), pages I79 185, it is disclosed that such image instability is caused by microdisplacements of the specimen holder in response to forces applied thereto and directed parallel to the support surface on which the specimen holder rests. Thus, after adjustment of the position of the specimen holder with respect to the particle beam is completed, the means utilized to adjust the position thereof must be positively decoupled from the holder to assure that forces are not applied to the specimen holder during observation or photographing of the image. Two structural arrangements for the realization of the above described objective are disclosed by the publicationv In one, push rods are coupled to the specimen holder by a member having adjustable stops, and a backlash of approximately lum is provided between the stops and specimen holder. This arrangement has the disadvantage that precise mechanical force and great care are necessary to adjust the position of the specimen holder. In the other arrangement, a coupling ring is connected without backlash to an adjustment means, and is drawn against the specimen holder vertically by the force of tension springs, and disengaged therefrom by means of adjustment levers. Thus, when the coupling member or ring is coupled to the specimen holder, a considerable force is exerted thereon since the force must be large enough in magnitude to assure sufficient contact between the holder and member or ring to effect adjustment of the specimen holder. The variation in the applied force which results during the coupling and decoupling of the coupling ring or member and the holder adjusting means causes irregular movement of the specimen holder which results in movement of the image observed.

SUMMARY OF THE INVENTION It is therefore an object of the invention to provide an adjustment mechanism for a charged particle beam apparatus which overcomes the aforementioned disadvantages of prior art devices. This and other objects are achieved by the provision of an adjustment mechanism in such apparatus which comprises a support surface disposed within the apparatus perpendicular to the beam axis, and a specimen holder disposed on the support surface and moveable transversely with respect to the axis. The holder includes apertures extending therethrough in a direction parallel to the beam axis in which bearing means are disposed. The bearing means engage the support surface and have a dimension which is greater than that of the specimen holder in the direction of the beam axis and less than that of the aperture in the direction perpendicular thereto. A coupling plate is disposed on the bearing means adjacent the specimen holder and coupled to an adjustment means which is operable externally of the apparatus, for adjusting the position of the plate, and thereby the specimen holder, with respect to the beam axis.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of an adjustment mechanism constructed according to the invention; and

FIG. 2 is a top sectional view of the adjustment mechanism, taken along section 2-2 of FIG. 1.

DETAILED DESCRIPTION Referring now to the drawings, a charged particle beam apparatus includes a housing 1 containing a vacuumv Within the housing, a specimen holder 3 is disposed on the support surface of an upper pole piece 2 of an objective lens of the apparatus. The specimen holder is disposed perpendicular to the particle beam axis 4, and frictionally engages the support surface. The holder is moveable transversely with respect to beam axis 4 on the support surface. A specimen cartridge 5, which carries a specimen at the point designated 6, is disposed within the specimen holder. A coil spring 7, disposed between the housing I and the specimen holder, presses the latter against the support surface of the pole piece 2. Apertures 9, illustrated as being circular in shape, extend through the specimen holder in a direction parallel to the beam axis, and receive bearing means, illustrated as ball bearings 8, which have a dimension which is greater than that of the specimen holder in the direction of the beam axis and less than that of the apertures in the direction perpendicular thereto. A coupling plate 10 is disposed over specimen holder 3 on bearings 8 and is pressed thereagainst by coil springs 11 disposed at the periphery of the plate.

As illustrated in FIG. 2, a third aperture 16, also circular in shape, and a third ball bearing 15, may also be provided for supporting the coupling plate. The preferred tolerance between ball bearings 8 and apertures 9 is approximately 10 X l0m. However, the tolerance between ball bearing 15 and aperture I6 may be arbitrary. This is so since ball bearing 15 has no function as a guide for the specimen holder. An adjustment means, illustrated as a pair of moveable adjustment rods 12 and 13, are disposed through housing 1 and engage coupling plate 10. The end 12a of rod 12 is tapered and is disposed in a conical recess provided in the edge of coupling plate 10, while adjustment rod 13 is provided with a roller 13a at the end thereof which engages a planar edgewise surface 13b on coupling plate I0. Adjustment rod 12 moves coupling plate 10 linearly in the X direction, while rod 13 moves plate 10 arcuately in the Y direction. A tension spring 14, coupled to housing 1 and the coupling plate, maintains constant contact between the plate and the adjustment rods. It should be noted that in lieu of the arrangement illustrated, an exact cross-slide arrangement of the type known in the art may also be utilized to adjust the position of coupling plate 10.

In operation, if either of the adjustment rods 12 or 13 is moved, coupling plate I0 is moved in response thereto and rolls on ball bearings 8, and, if provided, 15. After moving through a distance of a few micrometers, the ball bearings engage the edges of the apertures in the specimen holder. and move specimen holder 3 along therewith. As soon as the specimen holder is moved to its desired position, the adjustment rods are retracted slightly so that the ball bearings no longer engage the edges of the apertures in the holder. This effectively decouples the adjustment mechanism from the specimen holder, and prevents the application of moving forces in the direction parallel to the support surface. Movement of the image observed is thereby obviated.

The adjustment mechanism described has application to electron microscopes, ion microscopes, charged particle defraction equipment, and charged particle beam machining equipment. Also, the adjustment mechanism may be utilized to position other than conventional specimen holders in such an apparatus. For example, the mechanism may be used to adjust the position of a diaphragm in a charged particle beam apparatus.

In the foregoing, the invention has been illustrated and described with reference to specific exemplary embodiments thereof. However, it will be evident to those persons skilled in the art that many changes and modifications may be made thereunto without departing from the broader spirit and scope of the invention as set forth in the appended claims. The drawings and specification are therefore to be considered in an illustrative rather than in a restrictive sense.

What is claimed is:

l. A specimen holder adjustment mechanism for a charged particle beam apparatus, comprising:

a support surface disposed within the apparatus perpendicular to the beam axis;

a specimen holder, disposed on said support surface, and moveable transversely with respect to said beam axis, said holder including apertures extending therethrough in a direction parallel to the beam axis;

bearing means, disposed in said holder apertures and engaging said support surface, said bearing means having a dimension which is greater than that of said holder in the direction of said beam axis and less than that of said apertures in the direction perpendicular to said beam axis;

a coupling plate disposed on said bearing means adjacent said specimen holder; and

means, coupled to said plate and operable externally of the apparatus, for adjusting the position of said plate, and thereby said holder, with respect to said axis.

2. The adjustment mechanism recited in claim 1, wherein said apertures are circular in shape and said bearing means comprises ball bearings, the diameter of said ball bearings being about 10 X 10*m less than the diameter of said apertures. 

1. A specimen holder adjustment mechanism for a charged particle beam apparatus, comprising: a support surface disposed within the apparatus perpendicular to the beam axis; a specimen holder, disposed on said support surface, and moveable transversely with respect to said beam axis, said holder including apertures extending therethrough in a direction parallel to the beam axis; bearing means, disposed in said holder apertures and engaging said support surface, said bearing means having a dimension which is greater than that of said holder in the direction of said beam axis and less than that of said apertures in the direction perpendicular to said beam axis; a coupling plate disposed on said bearing means adjacent said specimen holder; and means, coupled to said plate and operable externally of the apparatus, for adjusting the position of said plate, and thereby said holder, with respect to said axis.
 2. The adjustment mechanism recited in claim 1, wherein said apertures are circular in shape and said bearing means comprises ball bearings, the diameter of said ball bearings being about 10 X 10 6m less than the diameter of said apertures. 